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Emergent respiratory viral pathogens

Jartii et al provide an excellent review new viral respiratory infections in the May 2012 Current Opinion in Pulmonary Medicine in you are looking for a concise update on this topic.  Here are some key points:

1. Human metapneumovirus (MPV) causes upper and lower respiratory tract infections in all ages but particularly in young children where the prevalence in respiratory infections is about 5% (cf. 2-5% in adults).  Overall, MPV infections are less or similar in severity to RSV or influenza virus infections. The most severe infections include bronchiolitis, exacerbations of asthma, and pneumonia. Although adults usually have only minor symptoms, MPV may cause serious morbidity and mortality in the elderly in long-term care facilities. MPV is a single-stranded envelped RNA virus in the family Paramyxoviridae and is most closely related to RSV genetically and clinically. Diagnosis is based on PCR but IF assays are now available.
2. New coronaviruses NL63 and HKU1 have been identified in a small percentage of individuals of all ages but have primarily been associated with mild upper respiratory tract infections. Chronic disease, immunosuppression, institutionalization and old age increase the risk of severe infection. CoVs are large plus-strand enveloped RNA viruses; currently, diagnosis of CoV-NL63 and -HKU1 is made only with RT-PCR.
3. Human bocaviruses (HBoV) include 4 species and belong to the Parvoviridae family. HBoVs are minute non-enveloped linear single-strand DNA viruses. HBoV1 shows a predilection for children and has been associated with upper and lower respiratory tract infections, acute asthma and pneumonia in children. Diagnosis is based on serology or PCR in serum due to persistence of HBoV DNA in nasophayngeal secretions.
4. Human rhinovirus (HRV) is the most common respiratory pathogen in all ages but PCR techniques have facilitated the discovery of two new groups, C and D, and possibly over 50 new HRV strains have been discovered in addition to the two former major genetic groups, A and B, and 99 HRV serotypes. HRV-C appears to be highly clinically significant. HRVs are small nonenveloped minus- sensed RNA viruses belonging to Picornaviridae. Diagnosis is based on PCR.
5. KI and WU polyomaviruses are newly discovered polyomaviruses that may be a cause of respiratory infections in children. Torque Teno Viruses are another newly discovered group of highly diverse viruses. High TTV loads in nasal secretions or plasma have positively correlated with markers of eosinophilic inflammation, bronchiectasis and idiopathic pulmonary fibrosis, congenital mannose-binding lectin deficiencies, and autoimmune rheumatoid disease.
6. All of these "new" respiratory viruses can be detected with PCR-based methodologies. But, since there is neither a specific treatment or vaccine for these viral infections, there really isn't a clinical need for diagnostic testing. Testing could be practical, however, in isolating infected patients in hospitals or LTC settings and in decreasing unnecessary antibiotic therapy. Quantitative PCR techiniques may be useful in establishing viral detection as the cause of respiratory illness.

Exosomes as Possible Biomarker for Tuberculosis

I have previously posted on exosomes in the context of cancer.  Here is a very interesting and brief video from Dr. Jeffrey Schorey regarding exosomes in the pathogenesis of tuberculosis and their possible use as a biomarker for infection.  It's only 5 minutes--go ahead and enjoy!

More on granulomatous lung disease: Pneumocystis jiroveci

Speaking of granulomatous lung disease (previous post), Hartel et al. have written a clinicopathologic review of the largest published series (20) of cases of pulmonary granulomatous inflammation associated with Pneumocystits jiroveci (formerly known as Prince).

I recall first seeing a case of Pneumocystis pulmonary granulomatous inflammation in an Illinois Registry of Anatomic Pathology case probably about 17-18 years ago--apparently, it made quite an impression!  Of course, I've only seen one similar case since them "in real life."

Several important findings from the paper:

1. The granulomas were well-formed in 80% of cases, necrotizing in 80% of cases, and multiple in 90% of cases.
2. Radiographic appearance is atypical for Pneumocystis pneumonia: Nodular infiltrates were present in 50% (8/16) of cases with studies and a solitary nodule was present in 19% of cases (3/16).
3. Open biopsy was required to make the diagnosis in 65% of cases and the diagnosis was made at autopsy in 25%.  Bronchoalveolar lavage--the main diagnostic tool in conventional Pneumocystis pneumonia--is of low yield in the diagnosis of granulomatous Pneumocystis pneumonia--as are bronchial washings, FNA, and transbronchial biopsy.  The fact that these tests are usually negative in this setting may explain why the diagnosis was made post-mortem a quarter of the time.
4. The authors discuss the role of host factors as most likely contributing to the atypical pathological manifestations of Pneumocystis since studies have repeatedly concluded that identical organisms are present in the various histologic reactions identified.
5. Good discussion of distinguishing between P. jiroveci and H. capsulatum on GMS stain: the lack of budding forms, shape and size (Pneumocystis--spherical, Histoplasma--ovoid)of yeast, and size of capsular dots (larger in Pneumocystis versus Histoplasma).